CN110476346B

CN110476346B - Rotating switching strategy for power converters

Info

Publication number: CN110476346B
Application number: CN201780088478.6A
Authority: CN
Inventors: 东栋; R.G.瓦戈纳; G.贾里雷迪; R.N.拉朱; 周锐
Original assignee: General Electric Co
Current assignee: General Electric Renovables Espana SL
Priority date: 2017-01-13
Filing date: 2017-12-20
Publication date: 2021-11-19
Anticipated expiration: 2037-12-20
Also published as: US10186995B2; WO2018132236A1; CN110476346A; US20180205334A1; EP3568908A4; EP3568908A1

Abstract

Systems and methods for operating a power converter having a plurality of inverter blocks with silicon carbide MOSFETs are provided. The DC-AC converter may include a plurality of inverter blocks. Each inverter block may include a plurality of switching devices. The control method may include identifying, for each inverter block, one of a plurality of switching patterns for operation of the inverter block. Each switching pattern may include a plurality of switching commands. The control method may further include controlling each inverter block based on the identified switching pattern for the inverter block. The control method may further include rotating the switching pattern among a plurality of inverter blocks.

Description

Rotating switching strategy for power converters

Technical Field

The present subject matter relates generally to power systems, and more particularly to systems and methods for a commutating switching strategy to reduce overall electrical losses and also balance power losses in power converter modular cascaded H-bridges with high frequency transformers.

Background

Power generation systems may use power converters to convert power into a form of power suitable for a power grid. In a typical power converter, a plurality of switching devices, such as insulated gate bipolar transistors ("IGBTs") or metal oxide semiconductor field effect transistors ("MOSFETs"), may be used in an electronic circuit, such as a half-bridge or full-bridge circuit, to convert power. Recent advances in switching device technology have allowed the use of silicon carbide ("SiC") MOSFETs in power converters. The use of SiC MOSFETs allows the power converter to operate at much higher switching frequencies than conventional IGBTs.

Disclosure of Invention

Aspects and advantages of embodiments of the present disclosure will be set forth in part in the description which follows, or may be learned by practice of the embodiments.

One exemplary aspect of the present disclosure relates to a control method for operating a DC-AC converter. The DC-AC converter may comprise a plurality of inverter blocks (blocks). Each inverter block may include one or more silicon carbide MOSFETs. The control method may include identifying, for each inverter block, one of a plurality of switching patterns for operation of the inverter block. Each switching pattern may include a plurality of switching commands. The control method may include controlling each inverter block based on the identified switching pattern for the inverter block. The control method may include rotating the switching pattern among a plurality of inverter blocks.

Another exemplary aspect of the present disclosure relates to a power conversion system. The power conversion system may include a DC-AC converter including a plurality of inverter blocks. Each inverter block may include one or more silicon carbide MOSFETs. The power conversion system may also include a control system configured to control operation of the DC-AC converter. The control system may be configured to identify one of a plurality of switching patterns for operation of each inverter block. Each switching pattern may include a plurality of switching commands. The control system may be further configured to control each inverter block based on the identified switching pattern for the inverter block. The control system may be further configured to rotate the switching pattern among the plurality of inverter blocks.

Another exemplary aspect of the present disclosure relates to a wind power generation system. The wind power generation system may include a wind generator configured to generate AC power and an AC-DC converter coupled to the wind generator. The AC-DC converter may be configured to convert AC power from the wind turbine into DC power. The wind power generation system may further comprise a DC link coupled to the AC-DC converter. The DC link may be configured to receive DC power from the AC-DC converter. The wind power system may further comprise a DC-AC converter coupled to the DC link. The DC-AC converter may be configured to receive DC power from the DC link. The DC-AC converter may include a plurality of inverter blocks. Each inverter block may include one or more silicon carbide MOSFETs. The wind power generation system may further comprise a control system configured to control the operation of the DC-AC converter. The control system may be configured to identify one of a plurality of switching patterns for operation of each inverter block. Each switching pattern may include a plurality of switching commands. The control system may be further configured to control each inverter block based on the identified switching pattern for the inverter block. The control system may be further configured to rotate the switching pattern among the plurality of inverter blocks.

Variations and modifications may be made to these exemplary aspects of the disclosure.

These and other features, aspects, and advantages of various embodiments will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the relevant principles.

Drawings

A detailed discussion of embodiments directed to one of ordinary skill in the art is set forth in the specification, which makes reference to the appended drawings, in which:

FIG. 1 depicts an exemplary wind power generation system;

fig. 2 depicts example elements for use in a power converter, according to an example aspect of the present disclosure;

FIG. 3 depicts a power converter according to an exemplary aspect of the present disclosure;

FIG. 4 depicts an exemplary switching strategy in accordance with an exemplary aspect of the present disclosure;

FIG. 5 depicts an exemplary switching strategy according to an exemplary aspect of the present disclosure;

FIG. 6 depicts an exemplary switching strategy according to an exemplary aspect of the present disclosure;

FIG. 7 depicts an exemplary method according to an exemplary aspect of the present disclosure; and

fig. 8 depicts elements suitable for use in a control device according to an exemplary aspect of the present disclosure.

Detailed Description

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. The various examples are provided by way of illustration of the invention and not by way of limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

Exemplary aspects of the present disclosure relate to systems and methods for a commutating switching strategy for power converters utilizing SiC MOSFETs. For example, power generation systems, such as systems that use a doubly-fed induction generator ("DFIG") as a power generation unit, may use one or more power converters to convert power from low-voltage multi-phase ac power to medium-voltage multi-phase ac power. As used herein, the "LV" voltage may be a power of less than about 1.5 kilovolts. As used herein, the "MV" voltage may be a power greater than about 1.5 kilovolts and less than about 100 kilovolts. As used herein, the term "about" may mean within 20% of the stated value.

In an embodiment, the power converter may be a multi-phase (e.g., three-phase) power converter configured to convert multi-phase power output from the generator. The power converter may include, for example, a first power converter configured to convert AC power output from a generator (such as a DFIG) to DC power and provide the DC power to a DC link. The second power converter may be configured to convert DC power from the DC link to AC power suitable for use on the grid. For example, the second power converter may be a DC-AC power converter and SiC MOSFETs may be utilized as power semiconductors, thereby allowing for very high switching frequencies.

The second power converter may include, for example, a plurality of inverter blocks. Each inverter block may include a plurality of bridge circuits configured to convert power, and each bridge circuit may include one or more SiC MOSFETs as switching devices. For example, each inverter block may be a DC-AC inverter block, and a plurality of inverter blocks may be coupled in parallel on the LV side and coupled in series on the MV side. Each DC-AC inverter block may include a first DC-AC conversion entity configured to convert LV DC power from the DC link to a high frequency LV AC voltage, an isolation transformer configured to provide isolation, a second AC-DC conversion entity configured to convert LV AC power to LV DC power, and a third DC-AC conversion entity configured to convert the LV DC power to LV AC power suitable for use on the grid. A plurality of inverter blocks may be connected in series to build the MV AC voltage suitable for use on the MV AC power grid.

In a popular modulation strategy, the inverter blocks may be configured in a cascaded H-bridge topology, where a switching pattern is used to control the individual inverter blocks to operate the switching devices in the inverter blocks. For example, in a cascaded H-bridge topology, the switching angles for the individual inverter blocks may be predetermined in order to obtain a desired waveform of the output of the power converter. When individual inverter blocks are turned on and off, the inverter blocks may contribute to the output waveform provided by the power converter. However, in such a cascaded H-bridge topology, the power handled by the individual inverter blocks may not be equal.

For example, a first inverter block in a power converter may be controlled using a switching pattern in which the first inverter block is the first inverter block to be turned on. Conversely, a second inverter block in the power converter may be controlled using a switching pattern in which the second inverter block is the last inverter block to be turned on. In such a configuration, the first inverter block may handle more power than the second inverter block. As a result, losses across the individual inverter blocks and temperatures of the inverter blocks in the power converter may be unbalanced. Furthermore, the thermal constraints of individual inverter blocks handling more power than other inverter blocks in the power converter may therefore be limiting constraints on the power converter. In addition, since the losses in the inverter block may be due to resistive heating of elements in the inverter block, the thermal load on the inverter block that handles more power than other inverter blocks may be higher than the thermal load on other inverter blocks. In such a configuration, the cooling system for the power converter may have to account for unbalanced thermal loads on the entire individual inverter blocks, or be designed to provide sufficient cooling to all inverter blocks based on the thermal load of the inverter block handling the most power.

Exemplary aspects of the present disclosure relate to systems and methods of rotating switching patterns among inverter blocks in a power converter to more evenly balance power conversion in the power converter. For example, systems and methods according to exemplary aspects of the present disclosure may allow multiple switching patterns to be rotated among multiple inverter blocks in a power converter. For example, the control device may identify one of a plurality of switching patterns for controlling operation of the individual inverter blocks. Each switching pattern may include a plurality of switching commands to operate one or more switching devices in the inverter block. The switching device may be, for example, a SiC MOSFET. The control device may further control each inverter block based on the identified switching pattern for each inverter block. For example, the control device may provide one or more switching commands to the individual inverter blocks such that the inverter blocks are switched according to the switching patterns that have been identified for the inverter blocks. In addition, the control device may rotate the switching pattern among the plurality of inverter blocks.

For example, the power converter may include six inverter blocks, a first inverter block, a second inverter block, a third inverter block, a fourth inverter block, a fifth inverter block, and a sixth inverter block. Further, the control device may identify six switching patterns to control switching of six inverter blocks of the power converter. Individual inverter blocks may be controlled based on the identified switching patterns for the inverter blocks. For example, a first inverter block may be controlled according to a first switching pattern, a second inverter block may be controlled according to a second switching pattern, and so on. According to an exemplary aspect of the present disclosure, the switching patterns may be rotated among a plurality of inverter blocks.

For example, in an embodiment, the switching patterns may be rotated among all inverter blocks, such as by rotating a first switching pattern to a second inverter block, rotating a second switching pattern to a third inverter block, rotating a third switching pattern to a fourth inverter block, and so on. Within each rotation interval, the switching pattern for an inverter block may be rotated to the next successive inverter block. In another embodiment, the two switching patterns may be alternated between two inverter blocks in the power converter. For example, the first switching pattern may be rotated from the first inverter block to the sixth inverter block, and the sixth switching pattern may be rotated from the sixth inverter block to the first inverter block. Similarly, the second and fifth inverter blocks and the third and fourth inverter blocks may have their switching patterns rotated. During the next successive toggle interval, the inverter block may toggle the switching pattern back. For example, the first switching pattern may be rotated from the sixth inverter block back to the first inverter block, and the sixth switching pattern may be rotated from the first inverter block back to the sixth inverter block. Other toggle switch type configurations may similarly be used.

In an embodiment, the switching pattern for at least one of the plurality of inverter blocks may be a pulse width modulation ("PWM") switching pattern to regulate line current from the DC-AC converter. Furthermore, the switching pattern for all other inverter blocks not under the PWM switching pattern may be a switching pattern comprising switching commands to output zero voltage or all positive or all negative voltage through the inverter blocks. Thus, one or more inverter blocks may regulate line current, while all other inverter blocks in the power converter may be turned on and off to contribute to the overall voltage of the power converter.

In an embodiment, the switching pattern may be rotated once every half cycle among the plurality of inverter blocks. For example, the switching pattern between two inverter blocks may be exchanged once every half-cycle between the two inverter blocks, or the switching pattern may be continuously rotated between all inverter blocks every half-cycle.

In an embodiment, the control device may receive one or more signals indicative of a temperature of one or more of the plurality of inverter blocks. For example, one or more temperature sensors may be configured to measure the temperature of each inverter block. The temperature sensors may provide temperature measurements to a control device, which may then rotate the switching pattern among the plurality of inverter blocks based at least in part on one or more signals indicative of the temperature of one or more inverter blocks. For example, if a particular inverter block is operating at a higher temperature than all other inverter blocks in the power converter, the control device may rotate the switching pattern among the plurality of inverter blocks so that the inverter block operating at the higher temperature may be controlled by the switching pattern to reduce the temperature of the inverter block (such as by controlling the inverter module with a switching pattern that handles less power than other switching patterns in the plurality of switching patterns).

In an embodiment, the switching patterns may be rotated among the banks formed by the plurality of inverters such that the average power handled by each inverter bank is approximately equal. As used herein, the term "approximately" means within plus or minus ten percent of the stated value. For example, the plurality of switching patterns may be rotated among the plurality of inverter blocks such that each of the plurality of switching patterns is used to control each inverter block for approximately the same amount of time. In such a configuration, each inverter block will handle approximately the same amount of power as all other inverter blocks in the power converter.

In this way, systems and methods according to exemplary aspects of the present disclosure may have the technical effect of allowing balancing of power losses across an entire inverter block in a power converter. Furthermore, this may normalize the average power and thermal load processed among the inverter blocks. Additionally, this may help ensure that the power converter is not limited by thermal constraints from individual inverter blocks in the power converter, which may allow all inverter blocks to operate at an increased power rating while satisfying the thermal constraints of the inverter blocks. Furthermore, this may reduce the number of inverter blocks needed to meet a particular power rating for the power converter, which may improve the reliability of the power converter by reducing the number of components in the system.

Referring now to the drawings, exemplary aspects of the disclosure will be discussed in more detail. FIG. 1 depicts a wind power system 100 including a DFIG 120 according to an exemplary aspect of the present disclosure. For purposes of illustration and discussion, the present disclosure will be discussed with reference to the exemplary wind power generation system 100 of FIG. 1. Those of ordinary skill in the art having access to the disclosure provided herein will appreciate that aspects of the present disclosure may also be applicable in other systems, such as full power conversion wind turbine systems, solar power systems, energy storage systems, and other power systems.

In exemplary wind power generation system 100, rotor 106 includes a plurality of rotor blades 108, which rotor blades 108 are coupled to a rotating hub 110 and together define a propeller. The propeller is coupled to an optional gearbox 118, which gearbox 118 is in turn coupled to a generator 120. According to aspects of the present disclosure, the generator 120 is a doubly-fed induction generator (DFIG) 120.

DFIG 120 is typically coupled to stator bus 154 and to power converter 162 via rotor bus 156. The stator bus provides output multi-phase power (e.g., three-phase power) from the stator of the DFIG 120, and the rotor bus 156 provides output multi-phase power (e.g., three-phase power) of the DFIG 120. Power converter 162 may be a bi-directional power converter configured to provide output power to power grid 184 and/or receive power from power grid 184. As shown, DFIG 120 is coupled to a rotor-side converter 166 via a rotor bus 156. Rotor-side converter 166 is coupled to line-side converter 168, which line-side converter 168 is in turn coupled to line-side bus 188. An auxiliary power feed (not depicted) may be coupled to the line-side bus 188 to provide power to components used in the wind power generation system 100, such as fans, pumps, motors, and other components.

In an exemplary configuration, rotor-side converter 166 and/or line-side converter 168 are configured for a normal mode of operation in a three-phase Pulse Width Modulation (PWM) arrangement using SiC MOSFETs and/or IGBTs as switching devices. Compared to conventional IGBTs, SiC MOSFETs can switch at very high frequencies. For example, SiC MOSFETs may switch at frequencies from approximately 0.01 Hz to 10 MHz, with typical switching frequencies being 1 KHz to 400 KHz, while IGBTs may switch at frequencies from approximately 0.01 Hz to 200 KHz, with typical switching frequencies being 1 KHz to 20 KHz. In addition, SiC MOSFETs may provide advantages over ordinary MOSFETs when operated in some voltage ranges. For example, in power converters operating at 1200V-1700V on the LV side, SiC MOSFETs have lower switching losses than normal MOSFETs.

In some embodiments, as will be discussed in more detail with respect to fig. 2 and 3, the rotor-side converter 166 and/or the line-side converter 168 may include a plurality of conversion modules that are each associated with a phase of the multi-phase power output of the generator. The rotor-side converter 166 and the line-side converter 168 may be coupled via a DC link 126, and a DC link capacitor 138 may span the DC link 126.

The power converter 162 may be coupled to a control device 174 to control the operation of the rotor-side converter 166 and the line-side converter 168. It should be noted that in the exemplary embodiment, control device 174 is configured as an interface between power converter 162 and control system 176.

In operation, power generated at DFIG 120 by rotating rotor 106 is provided to grid 184 via dual paths. The dual paths are defined by a stator bus 154 and a rotor bus 156. On the stator bus 154 side, sinusoidal multi-phases (e.g., three phases) are provided to a power delivery point (e.g., grid 184). In particular, the AC power provided via the stator bus 154 may be medium voltage ("MV") AC power. On the rotor bus side 156, sinusoidal multi-phase (e.g., three-phase) AC power is provided to a power converter 162. In particular, the AC power provided to the power converter 162 via the rotor bus 156 may be low voltage ("LV") AC power. Rotor-side power converter 166 converts the LV AC power provided from rotor bus 156 to DC power and provides the DC power to DC link 126. Switching devices (e.g., SiC MOSFETs and/or IGBTs) used in the parallel bridge circuit of rotor-side power converter 166 may be modulated to convert AC power provided from rotor bus 156 to DC power suitable for DC link 126. Such DC power may be LV DC power.

In wind power generation system 100, power converter 162 may be configured to convert LV AC power to MV AC power. For example, line-side converter 168 may convert LV DC power on DC link 126 to MV AC power suitable for grid 184. In particular, the SiC MOSFETs used in the bridge circuits of line-side power converter 168 may be modulated to convert DC power on DC link 126 to AC power on line-side bus 188. SiC MOSFETs can operate at higher switching frequencies than conventional IGBTs. Additionally, one or more isolation transformers coupled to one or more of the bridge circuits may be configured to step up or down the voltage from the DC link as needed. Additionally, multiple inverter blocks may be connected in series on the MV side to collectively step up the voltage of the power on the DC link 126 to MV AC power. The MV AC power from power converter 162 may be combined with MV power from the stator of DFIG 120 to provide multi-phase power (e.g., three-phase power) having a frequency substantially maintained at the frequency of grid 184 (e.g., 50 Hz/60 Hz). In this manner, MV line-side bus 188 may be coupled to MV stator bus 154 to provide such multi-phase power.

Various circuit breakers and switches (such as circuit breaker 182, stator synchronizing switch 158, etc.) may be included in wind power generation system 100 for isolating various components as necessary for normal operation of DFIG 120 during connection to and disconnection from grid 184. In this manner, such components may be configured to connect or disconnect the corresponding bus, for example, when the current is excessive and may damage components of the wind power generation system 100 or for other operational considerations. Additional protective components may also be included in the wind power generation system 100. For example, as depicted in FIG. 1, a multi-phase crowbar (crowbar) circuit 190 may be included to prevent an overvoltage condition that damages the circuitry of wind power generation system 100.

The power converter 162 may receive control signals from, for example, a control system 176 via a control device 174. The control signal may be based on, inter alia, a sensed condition or operational characteristic of the wind power generation system 100. Typically, the control signal provides control of the operation of the power converter 162. For example, feedback in the form of sensed speed of DFIG 120 may be used to control conversion of output power from rotor bus 156 to maintain a proper and balanced multi-phase (e.g., three-phase) power supply. Other feedback from other sensors (including, for example, stator and rotor bus voltage and current feedback) may also be used by the control device 174 to control the power converter 162. Various forms of feedback information may be used to generate the switch control signals (e.g., gate timing commands for the switching devices), the stator synchronization control signals, and the circuit breaker signals.

Referring now to fig. 2, a topology of components in a DC-AC converter is depicted. Fig. 2 depicts an exemplary DC-AC inverter block 206, as depicted in fig. 3, the DC-AC inverter block 206 may be included in the conversion module 200 of the line side converter 168. Each inverter block 206 may include a plurality of conversion entities. For example, the inverter block 206 may include a first conversion entity 212, a second conversion entity 214, and a third conversion entity 216. Each conversion entity 212-216 may comprise a plurality of bridge circuits coupled in parallel. For example, the conversion entity 216 includes a bridge circuit 218 and a bridge circuit 220. As indicated, each bridge circuit may include a plurality of switching devices coupled in series. For example, the bridge circuit 220 includes an upper switching device 222 and a lower switching device 224. The switching device may be a SiC MOSFET, which may operate at a higher switching frequency than a conventional IGBT. The switching devices may also be conventional IGBTs and/or MOSFETs. As shown, the inverter block 206 further includes an isolation transformer 226. Isolation transformer 226 may be coupled to conversion entity 212 and conversion entity 214. As shown, the inverter block 206 may further include

capacitors

228 and 230. For example, the capacitor 230 may be connected across the DC-link between the second conversion entity 214 and the third conversion entity 216.

The first conversion entity 212, the isolation transformer 226 and the second conversion entity 214 may together define an internal converter 240. The internal converter 240 is operable to convert LV DC power from the DC link 126 to LV DC power. In an embodiment, the internal converter 240 may be a high frequency resonant converter. In a resonant converter configuration, the resonant capacitor 232 may be included in the internal converter 240. In various embodiments, the resonant capacitor 232 may be included on the DC link side of the isolation transformer 226 (as depicted in fig. 2), on the grid side of the isolation transformer 226 (not depicted), or on both the DC link side and the grid side of the isolation transformer 226 (not depicted). In another embodiment, the internal converter 240 may be a hard-switched converter by removing the resonant capacitor 232. The third conversion entity 216 may also be referred to as an external converter 216. The external converter 216 may convert the LV DC power from the internal converter to LV AC power suitable for use on the grid 184. In a typical application, the external converter 216 may be a hard-switched converter, and therefore does not include a resonant capacitor.

Fig. 3 depicts an exemplary line-side converter 168 according to an exemplary embodiment of the present disclosure. As shown, the line-side converter 168 includes a conversion module 200, a conversion module 202, and a conversion module 204. The conversion module 200-204 may be configured to receive LV DC power from the rotor-side converter 166 and convert the LV DC power to MV AC power for feeding to the grid 184. Each conversion module 200-204 is associated with a single phase of three-phase output AC power. In particular, the conversion module 200 is associated with an a-phase output of the three-phase output power, the conversion module 202 is associated with a B-phase output of the three-phase output power, and the conversion module 204 is associated with a C-phase output of the three-phase output power.

Each conversion module 200-204 includes a plurality of inverter blocks 206-210. For example, as shown, conversion module 200 includes inverter block 206, inverter block 208, and inverter block 210. In embodiments, each conversion module 200-. The line-side converter 168 may be a bi-directional power converter. Line-side converter 168 may be configured to convert LV DC power to MV AC power and vice versa. For example, when providing power to grid 184, line-side converter 168 may be configured to receive LV DC power from DC link 126 on the LV side of line-side converter 168 and output MV AC power on the MV side of line-side converter 168. The inverter blocks 206-210 may be coupled together in parallel on the LV side and may be coupled together in series on the MV side.

In one particular exemplary embodiment, when providing power to grid 184, conversion entity 212 may be configured to convert LV DC on DC link 126 to LV AC power. Isolation transformer 226 may be configured to provide isolation. The conversion entity 214 may be configured to convert LV AC power to LV DC power. Conversion entity 216 may be configured to convert the LV DC power to LV AC power suitable for provision to grid 184. A plurality of inverter blocks may be connected in series to build the MV AC voltage suitable for use on the MV AC power grid.

The

inverter block

206 and 210 may be configured to contribute to the overall MV AC power provided by the conversion module 200. In this manner, any suitable number of inverter blocks may be included within the

conversion module

200 and 204. As indicated, each conversion module 200-204 is associated with a single phase of output power. In this way, the switching devices of the

conversion module

200 and 204 may be controlled using suitable gate timing commands (e.g., provided by one or more suitable driver circuits) to produce the appropriate phase of output power to be provided to the power grid. For example, the control device 174 may provide suitable gate timing commands to the gates of the switching devices of the bridge circuit. The gate timing commands may control pulse width modulation of the SiC MOSFETs and/or IGBTs to provide a desired output.

It will be appreciated that although fig. 3 depicts only the line-side converter 168, the rotor-side converter 166 depicted in fig. 2 may include the same or similar topology. In particular, rotor-side converter 166 may include a plurality of conversion modules having one or more conversion entities as described with reference to line-side converter 168. Further, it will be appreciated that the line-side converter 168 and the rotor-side converter 166 may include SiC MOSFETs, IGBT switching devices, and/or other suitable switching devices. In embodiments in which rotor-side converter 166 is implemented using SiC MOSFETs, rotor-side converter 166 may be coupled to a crowbar circuit (e.g., multi-phase crowbar circuit 190) to protect the SiC MOSFETs from high rotor currents during certain fault conditions.

Referring now to fig. 4, an example switching strategy is depicted in accordance with an example aspect of the present disclosure. Fig. 4 depicts a plurality of switching patterns that have been identified for a plurality of inverter blocks in a power converter. For example, a power converter (such as the line-side converter 168) may include a plurality of inverter blocks, such as the inverter blocks 206 and 210 depicted in fig. 2 and 3. As depicted, the power converter may include six inverter blocks, with each inverter block receiving an identified switching pattern 402. In an embodiment, the power converter may include two or more inverter blocks. For example, as depicted, the first inverter block 206A may have a first identified switching pattern 402A, the second inverter block 206B has a second identified switching pattern 402B, the third inverter block 206C may have a third identified switching pattern 402C, the fourth inverter block 206D may have a fourth identified switching pattern 402D, the fifth inverter block 206E may have a fifth identified switching pattern 402E, and the sixth inverter block 206F may have a sixth identified switching pattern 402F. In this way, the plurality of inverter blocks may each have an identified switching pattern from the plurality of switching patterns.

Each identified switching pattern 402 may include a plurality of gating commands. For example, the identified switching pattern 402A for the first inverter block may include an internal converter on/off command 404A for the internal converter 240 of the first inverter block. The internal converter on/off command 404A may be used to control the operation of a switching device (such as a SiC MOSFET) in the internal converter 240 such that power flows through the internal converter 240. For example, a "1" command may be a command to cause power to flow through the internal converter (i.e., turn the internal converter on), and a "0" command may be a command to prevent power from flowing through the internal converter (i.e., turn the internal converter off). Each identified switching pattern 402A-F may include an associated internal converter on/off command 404A-F, respectively.

Further, each identified switching pattern 402A-F may include an external converter duty cycle command 406 for an external converter (such as the external converter 216). For example, a first identified switching pattern 402A for first inverter block 206A may include a first external converter duty cycle command 406A to control the output voltage of the external converter 216. For example, the external converter 216 of the first inverter block 206A may provide a positive terminal voltage when the external converter duty cycle command 406A is greater than 0. If the external converter duty cycle command 406A is less than zero, the external converter 216 may provide a negative terminal voltage. The terminal voltage of the outer converter 216 of the first inverter block 206A may be equal to the duty cycle of the outer converter 216 multiplied by the DC link voltage ("Vdc") from the output of the inner converter 240 in the first inverter block 206A. Thus, when the external converter duty cycle command 406A is +1, the terminal voltage for the first inverter block may be + Vdc, and when the external converter duty cycle command 406A is-1, the terminal voltage for the first inverter block may be-Vdc. Similarly, the external converter duty cycle commands 406B-F may be used to control the external converter terminal voltages from each external converter 216 in the second through sixth inverter blocks 206B-F. Thus, each of the internal converter on/off command 404 and the external converter duty cycle command 406 may include multiple gating commands in the switching pattern 402.

In an embodiment, the identified switching pattern 402 for at least one inverter block 206 may be in a PWM switching pattern to regulate line current from the DC-AC converter. Furthermore, the identified switching pattern 402 for all other inverter blocks 206 not provided with PWM switching patterns may be a switching pattern that includes switching commands to output zero voltage or all positive or all negative voltage through the inverter blocks 206. For example, as depicted in fig. 4, at any point in time, only one inverter block 206 is provided with a PWM switching pattern. For example, in the identified switching pattern 402B provided to second inverter block 206B, when external duty cycle command 406B is a duty cycle that does not include a full voltage (positive or negative) or zero duty cycle command, external converter duty cycle command 406B is in a PWM pattern. As shown, during a time period in which the external converter duty cycle command 406B is non-zero (identified as time period "PWM B"), all other external converter duty cycle commands 406A and 406C-F include full voltage (positive or negative) or zero voltage duty cycle commands. Thus, at any point in time, at least one inverter block 206 may be regulating line current from the DC-AC converter.

Referring now to fig. 5, an example switching strategy is depicted in accordance with an example aspect of the present disclosure. Fig. 5 depicts a plurality of switching patterns that have been identified for a plurality of inverter blocks in a power converter. The same reference numerals are used to refer to the same or similar elements as those in fig. 4.

As shown in fig. 5, each identified switching pattern 402A-F may be used to control an associated inverter block. However, as shown in fig. 5, switching commands such as internal converter on/off commands 404 and external converter duty cycle commands 406 have been rotated among the plurality of inverter blocks 206. For example, as indicated by arrow "a," the first inner converter on/off command 404A and the first outer converter duty cycle command 406A have rotated from the first inverter bank 206A to the second inverter bank 206B. Similarly, the identified switching patterns 402B-F have been rotated to inverter blocks 206C-F and 206A, respectively, as indicated by arrows B-F. The identified switching pattern 402 may be rotated among the plurality of inverter blocks at a specified rotation interval, such as every half cycle. Further, the identified switching pattern 402 may be rotated to another successive inverter block during each successive rotation interval (such as during each half cycle). For example, in successive half cycles, the first identified switching pattern 402A may rotate from the first inverter block 206A to the second inverter block 206B, to the third inverter block 206C, to the fourth inverter block 206D, to the fifth inverter block 206E, to the sixth inverter block 206F, and back to the first inverter block 206A. Similarly, the second-sixth identified switching patterns 402B-F may be rotated by the inverter blocks 206A-F. In this way, the identified switching pattern may be rotated among the plurality of inverter blocks.

Referring now to fig. 6, an example switching strategy is depicted in accordance with an example aspect of the present disclosure. Fig. 6 depicts a plurality of switching patterns that have been identified for a plurality of inverter blocks in a power converter. The same reference numerals are used to refer to the same or similar elements as those in fig. 4 and 5.

As shown in fig. 6, each identified switching pattern 402A-F may be used to control an associated inverter block. However, as shown in fig. 5, switching commands such as on/off command 404 and external converter duty cycle command 406 have been rotated among the plurality of inverter blocks 206A-F such that the identified switching patterns for

inverter blocks

206A and 206F, inverter blocks 206B and 206E, and

inverter blocks

206C and 206D have been exchanged. For example, as indicated by arrow "a", the first inner converter on/off command 404A and the first outer converter duty cycle command 406A have been rotated from the first inverter block 206A to the sixth inverter block 206F, while, as indicated by arrow "F", the sixth inner converter on/off command 406F and the sixth outer converter duty cycle command 406F have been rotated from the sixth inverter block 206F to the first inverter block 206A. Similarly, the identified switching

patterns

402B and 402E have rotated among the second inverter block 206B and the fifth inverter block 206E, as indicated by arrows B and E, and the identified switching

patterns

402C and 402D have rotated among the third inverter block 206C and the fourth inverter block 206D, as indicated by arrows C and D. The identified switching pattern 402 may be rotated among the plurality of inverter blocks at a specified rotation interval, such as every half cycle. Further, the identified switching pattern 402 may be rotated back to the previous inverter block for each successive rotation interval (such as for each half cycle). For example, in successive half cycles, the first identified switching pattern 402A may rotate from the first inverter block 206A to the sixth inverter block 206F and back to the first inverter block 206A. Thus, each identified switching pattern 402 may alternate between two or more identified inverter chunks, e.g., each identified switching pattern 402 may alternate between two inverter chunks 206 at regular alternating intervals, as depicted in fig. 6. In this way, the identified switching pattern may be rotated among the plurality of inverter blocks.

Referring generally to fig. 4-6, the identified switching pattern 402 may be rotated among a plurality of inverter blocks based on one or more parameters. For example, in an embodiment, the switching patterns may be rotated among a plurality of inverter blocks such that the average power handled by each inverter block is approximately equal. For example, on average, each inverter block may be controlled by each of a plurality of switching patterns for approximately equal periods of time (such as if each switching pattern is rotated by each inverter block in the power converter). However, other rotation strategies may be similarly used, such as by rotating two subsets of the plurality of switching patterns among two subsets of inverter blocks (where the subsets of switching patterns handle approximately equal power) or other rotation switching strategies. In this manner, the identified switching patterns may be rotated among the plurality of inverter blocks such that the average power handled by each inverter block is approximately equal.

In an embodiment, one or more temperature sensors may be configured to measure temperatures associated with one or more inverter blocks. For example, the plurality of sensors may be configured to sense a temperature associated with each inverter block in the power converter, and may be configured to provide one or more signals indicative of the temperature of one or more inverter blocks to the control device. If an individual inverter block has a temperature that is higher than the temperatures of other blocks or if the temperature is higher than a threshold temperature, the switching pattern may be rotated among the plurality of inverter blocks based at least in part on the temperature measurements (such as, for example, by rotating the switching pattern in which relatively lower power is processed to the individual inverter block having the higher temperature). Similarly, inverter blocks with lower temperatures may be controlled by the switching pattern in which relatively more power is handled. In this manner, the switching pattern may be rotated among the plurality of inverter blocks based at least in part on one or more signals indicative of the temperature of one or more inverter blocks.

Referring now to fig. 7, an exemplary control method (600) for operating a DC-AC converter is depicted, according to an exemplary aspect of the present disclosure. The DC-AC converter may include a plurality of inverter blocks. Each inverter block may include one or more SiC MOSFETs. For example, each inverter block may be a DC-AC inverter block, which may include a first conversion entity, a second conversion entity, a third conversion entity, and an isolation transformer. Each conversion entity may comprise a plurality of bridge circuits, which may comprise one or more SiC MOSFETs. The DC-AC converter may be, for example, a line-side converter 168 in wind power generation system 100.

At (602), for each inverter block, the method (600) may include identifying one of a plurality of switching patterns for operation of the inverter block. Each switching pattern may include a plurality of switching commands. For example, each switching pattern may include an internal converter on/off command 404 and/or an external converter duty cycle command 406. Each inverter block (such as inverter block 206) may have an identified switching pattern (such as identified switching pattern 402) assigned to the inverter block.

At (604), the method (600) may include controlling the individual inverter chunks based on the identified switching patterns for the inverter chunks. For example, the control device 174 or the control system 176 may be configured to control one or more switching devices (such as one or more SiC MOSFETs) to allow power to flow through the inverter block based on the identified switching pattern. Further, multiple inverter blocks may be controlled to produce a desired output waveform (such as by using a PWM switching pattern for at least one of the inverter blocks, as described herein).

At (606), the method (600) may include rotating the switching pattern among a plurality of inverter blocks. For example, each inverter block (such as inverter blocks 206A-F) may have an identified switching pattern 402A-F. The identified switching patterns 402A-F may be rotated among the inverter chunks 206A-F by, for example, rotating a plurality of the identified switching patterns 402A-F among the respective inverter chunks 206A-F at successive intervals, such as at every half cycle. For example, as depicted in fig. 5, the identified switching patterns 402A-F may be rotated among the inverter blocks 206A-F at successive intervals. In an embodiment, the identified switching pattern 402 may be alternated between two or more inverter blocks 206. For example, as depicted in fig. 6, the first identified switching pattern 402A and the sixth identified switching pattern 402F may rotate among the first inverter block 206A and the sixth inverter block 206F at successive intervals (such as every half cycle). In an embodiment, the switching patterns may be rotated among a plurality of inverter blocks such that the average power handled by each inverter block is approximately equal.

At (608), the method (600) may include receiving one or more signals indicative of a temperature of one or more inverter blocks. For example, one or more temperature sensors may be configured to sense temperatures associated with one or more inverter blocks in the power converter. For example, each inverter block may have an associated temperature sensor configured to measure a temperature at each inverter block. The control device or control scheme may be configured to receive one or more signals indicative of the temperature of one or more inverter blocks from one or more temperature sensors.

At (610), the method (600) may include rotating the switching pattern among the plurality of inverter chunks based at least in part on one or more signals indicative of the temperature of one or more inverter chunks. For example, the power converter may include a plurality of inverter blocks, such as six inverter blocks 206A-F. Each inverter block 206A-F may have a temperature sensor associated with the inverter block and configured to measure the temperature of the inverter block. Signals indicative of the temperature of the inverter blocks (such as, for example, a temperature indicative of the first inverter block 206A being higher than the temperature of the inverter blocks 206B-F) may be used by the control device 174 or the control system 176 to rotate the pattern among the plurality of inverter blocks 206A-F. For example, the control device 174 or the control system 176 may identify a switching pattern 402A for the first inverter block 206A in which the average power processed is less than the average power in the other switching patterns of the plurality of switching patterns. The control device 174 or the control system 176 may alternate the plurality of switching patterns among the inverter blocks 206A-F such that the inverter block 206A is controlled by the switching pattern 402A. In this manner, the control device 174 or the control system 176 may alternate the switching pattern among the plurality of inverter chunks, and more specifically, alternate the switching pattern to change the temperature of one or more build chunks, based at least in part on one or more signals indicative of the temperature of one or more inverter chunks.

Fig. 8 depicts an example control apparatus 700 according to an example embodiment of the present disclosure. Control device 700 may be used, for example, as control device 174 or control system 176 in wind power generation system 100. The control device 700 may include one or more computing devices 710. Computing device(s) 710 may include one or more processors 710A and one or more storage devices 710B. The one or more processors 710A may include any suitable processing device, such as a microprocessor, micro-control device, integrated circuit, logic device, and/or other suitable processing device. The one or more storage devices 710B may include one or more computer-readable media including, but not limited to, non-transitory computer-readable media, RAM, ROM, hard drives, flash drives, and/or other storage devices.

The one or more storage devices 710B may store information accessible by the one or more processors 710A, including computer-readable instructions 710C executable by the one or more processors 710A. The instructions 710C may be any set of instructions that, when executed by the one or more processors 710A, cause the one or more processors 710A to perform operations. In some embodiments, the instructions 710C may be executable by the one or more processors 710A to cause the one or more processors 710A to perform operations, such as any operations and functions for which the computing system 700 and/or computing device(s) 710 are configured, operations for controlling a DC-AC converter as described herein (e.g., the method 600), and/or any other operations or functions of the one or more computing devices 710. The instructions 710C may be software written in any suitable programming language, or may be implemented in hardware. Additionally and/or alternatively, the instructions 710C may be executed in logically and/or physically separate threads on the processor(s) 710A. Storage device(s) 710B may further store data 710D accessible by processor(s) 710A. For example, data 710D may include data indicating: power flow, current flow, temperature, actual voltage, nominal voltage, gating commands, switching patterns, and/or any other data and/or information described herein.

Computing device(s) 710 may also include a network interface 710E for communicating (e.g., via a network) with other components of system 700, for example. Network interface 710E may include any suitable means for interfacing with one or more networks including, for example, a transmitter, receiver, port, control device, antenna, and/or other suitable means. For example, network interface 710E may be configured to communicate with one or more sensors (such as one or more voltage sensors or temperature sensors) in wind power generation system 100. Further, the network interface 710 may be configured to communicate with a control system (such as the control system 176) or a control device (such as the control device 174).

The techniques discussed herein make reference to computer-based systems and the actions taken by and information sent to and from the computer-based systems. Those of ordinary skill in the art will appreciate that the inherent flexibility of a computer-based system allows for a wide variety of possible configurations, combinations, and assignments of tasks and functions between and among the components. For example, the processes discussed herein may be implemented using a single computing device or multiple computing devices operating in combination. The databases, memories, instructions, and applications may be implemented on a single system or distributed across multiple systems. The distributed components may operate sequentially or in parallel.

For purposes of illustration and discussion, the present disclosure is discussed with reference to a DFIG power generation system including a power converter utilizing SiC MOSFETs. One of ordinary skill in the art, using the disclosure provided herein, will appreciate that other power generation systems and/or topologies may benefit from the exemplary aspects of the present disclosure. For example, the grounding and protection schemes disclosed herein may be used in wind power generation systems, solar power generation systems, gas turbine power generation systems, or other suitable power generation systems. Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A control method for operating a DC-AC converter comprising a plurality of inverter blocks, each inverter block comprising a plurality of switching devices, the method comprising:

identifying one of a plurality of switching patterns for operation of the inverter blocks for each inverter block, each switching pattern comprising a plurality of switching commands, wherein each inverter block of the plurality of inverter blocks comprises an internal converter and an external converter, and wherein the plurality of switching commands comprises: an internal converter on/off command to allow or disallow power flow through the internal converter, and an external converter duty cycle command to control an output voltage of the external converter, wherein the external converter duty cycle command includes a PWM switching pattern and a non-PWM switching pattern;

controlling each inverter block based on the identified switching pattern for the inverter block such that at a given point in time one of the plurality of inverter blocks regulates a line current of the DC-AC converter, wherein controlling each inverter block comprises applying the external converter duty cycle command to each inverter block, and wherein applying the external converter duty cycle command to each inverter block comprises:

at the given point in time, applying the PWM switching pattern to the one inverter block such that the line current from the DC-AC converter is regulated by the inverter block; and

at the given point in time, applying the non-PWM switching pattern to all other inverter blocks such that the all other inverter blocks output either zero voltage or full positive or full negative voltage; and

rotating the plurality of switching patterns among the plurality of inverter blocks, wherein inverter blocks of the plurality of inverter blocks are connected in series with each other at an AC side of the DC-AC converter.

2. The control method of claim 1, wherein at least one of the plurality of switching devices comprises a silicon carbide MOSFET.

3. The control method of claim 1, wherein rotating the plurality of switching patterns among the plurality of inverter blocks comprises rotating the plurality of switching patterns once every half cycle among the plurality of inverter blocks.

4. The control method according to claim 1, characterized in that the control method further comprises:

receiving one or more signals indicative of a temperature of one or more of the plurality of inverter blocks; and is

Wherein rotating the plurality of switching patterns among the plurality of inverter chunks comprises rotating the plurality of switching patterns among the plurality of inverter chunks based at least in part on the one or more signals indicative of the temperature of the one or more inverter chunks.

5. The control method of claim 1 wherein rotating the plurality of switching patterns among the plurality of inverter blocks comprises rotating the plurality of switching patterns among the plurality of inverter blocks such that average power handled by each inverter block is approximately equal.

6. The control method of claim 1, wherein the plurality of inverter blocks comprises a plurality of DC-AC inverter blocks.

7. The control method of claim 6, wherein each of the plurality of DC-DC-AC inverter blocks includes a first conversion entity, a second conversion entity, a third conversion entity, and an isolation transformer;

wherein the first conversion entity is a first DC-AC conversion entity;

wherein the second conversion entity is an AC-DC conversion entity;

wherein the isolation transformer is coupled between the first conversion entity and the second conversion entity; and is

Wherein the third conversion entity is a second DC-AC conversion entity.

8. The control method according to claim 1, characterized in that the DC-AC converter comprises a multi-phase DC-AC converter, wherein the control method is performed for each phase of the multi-phase power converted by the multi-phase DC-AC converter.

9. A power conversion system, comprising:

a DC-AC converter including a plurality of inverter blocks, each of the plurality of inverter blocks including an internal converter and an external converter, having one or more silicon carbide MOSFETs, wherein the inverter blocks of the plurality of inverter blocks are connected in series with each other at an AC side of the DC-AC converter; and

a control system coupled to the DC-AC converter and configured to;

identifying one of a plurality of switching patterns for operation of respective inverter blocks, each switching pattern comprising a plurality of switching commands, wherein the plurality of switching commands comprises: an internal converter on/off command to allow or disallow power flow through the internal converter, and an external converter duty cycle command to control an output voltage of the external converter, wherein the external converter duty cycle command includes a PWM switching pattern and a non-PWM switching pattern;

controlling each inverter block based on the identified switching pattern for the inverter block such that at a given point in time one of the plurality of inverter blocks regulates line current of the DC-AC converter, wherein to control each inverter block, the control system is configured to:

at the given point in time, applying the non-PWM switching pattern to all other inverter blocks such that the all other inverter blocks output either zero voltage or full positive or full negative voltage; and is

Rotating the plurality of switching patterns among the plurality of inverter blocks.

10. The power conversion system of claim 9, wherein the control system is configured to rotate the plurality of switching patterns once per half cycle among the plurality of inverter blocks.

11. The power conversion system of claim 9, wherein the control system is configured to receive one or more signals indicative of a temperature of one or more of the plurality of inverter blocks; and is

Wherein the control system is configured to rotate the plurality of switching patterns among the plurality of inverter chunks based at least in part on the one or more signals indicative of the temperature of the one or more inverter chunks.

12. The power conversion system of claim 9, wherein the control system is configured to rotate the plurality of switching patterns among the plurality of inverter blocks such that average power handled by each inverter block is approximately equal.

13. A wind power generation system, comprising:

a wind generator configured to generate AC power;

an AC-DC converter coupled to the wind generator, the AC-DC converter configured to convert the AC power from the wind generator to DC power;

a DC link coupled to the AC-DC converter, the DC link configured to receive DC power from the AC-DC converter;

a DC-AC converter coupled to the DC link, the DC-AC converter configured to receive DC power from the DC link; the DC-AC converter includes a plurality of inverter blocks, wherein inverter blocks of the plurality of inverter blocks are connected in series with each other at an AC side of the DC-AC converter, each inverter block of the plurality of inverter blocks including an inner converter and an outer converter, having one or more silicon carbide MOSFETs; and

a control system coupled to the DC-AC converter, wherein the control system is configured to:

14. The wind power system of claim 13, wherein the control system is configured to rotate the plurality of switching patterns once per half cycle among the plurality of inverter blocks.